Fail safe electro-magnetic lifting device with safety-stop means



United States Patent 3,316,514 FAIL SAFE ELECTRO-MAGNETIC LIFTING DE- VICE WITH SAFETY-STOP MEANS Raymond J. Radus, Monroeville, and Lawrence R. Scott,

Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 29, 1965, Ser. No. 443,331 4 Claims. '(Cl. 335-291) The present invention relates to lifting apparatus, and more particularly to lifting apparatus of the permanent magnet type.

Lifting or hoist apparatus utilizing electro-magnets have been in operation for many years. The electromagnet type of lifting apparatus has two severe disadvantages: (l) a large amount of energy must be supplied to the electro-magnet in order to generate a sufficient magnetic field to provide reasonable lifting weight capacity, and (2) the load will fall if the electromagnet is deenergized due to a power failure or other interruption of electrical power to a coil of the electromagnet. The latter disadvantage makes such apparatus dangerous or requires additional safety features to insure the load will not accidentally be dropped. The use of a permanent magnet for the lifting apparatus would be particularly advantageous from an energy standpoint. However, the difiiculty of disengaging the load from the permanent magnet must be overcome. Also, safety must be considered if the permanent magnet is to be made fail safe.

In copending applications, Ser. No. 167,360, filed Jan. 19, 1962, entitled, Magnetic Memory Device, and Ser. No. 283,035, filed May 24, 1963, entitled, Permanent Magnet Memory Device Using Pulse Control, both by Raymond J. Radus and assigned to the same assignee as the present application, permanent magnet devices are shown in which the attractive magnetic force of a permanent magnet may be bistably switched between different magnetic circuits of the device. The switching between the high and low attractive force circuits of the memory device is accomplished by the application of a low energy electrical signal to an electro-magnetic coil disposed in one or more of the magnetic circuits. The device will remain in one of its bistable states until a control signal is applied to switch another of the magnetic circuits to a higher or lower reluctance than the reference magnetic circuit. Lifting apparatus which could incorporate such a device would be highly advantageous in that the device requires only the momentary use of a very low energy source which is used only for switching. Moreover, if a hoist using permanent magnet devices can be made fail safe such lifting apparatus would overcome both of the serious problems encountered in the electro-magnetic type of lifting apparatus.

It is, therefore, an object of the present invention to provide new and improved lifting apparatus utilizing permanent magnet devices.

It is a further object of the present invention to provide new and improved lifting apparatus utilizing permanent magnet memory devices in which the engaging or disengaging of a load may be accomplished by a low level energy source.

It is a still further object of the present invention to provide new and improved lifting apparatus utilizing permanent magnet memory devices and which incorporates therein a fail safe feature prohibiting the accidental dropping of a load once engaged.

Broadly, the present invention provides lifting apparatus in which a permanent magnet device is provided wherein a high attractive force may be switched from one magnetic circuit of the device to another magnetic circuit of the device through the use of a control winding. When lifting is desired, the high attractive magnetic force is switched to the end of the device adjacent the load to be lifted. Safety means are provided to prevent the accidental dropping of the load during the moving operation.

These and other objects and advantages of the present invention will become more apparent when considered in view of the following specification and drawings, in which:

FIGURE 1 is a pictorial diagram of the lifting apparatus of the present invention; and

FIGS. 2, 3, 4 and 5 are front elevation views of the present lifting apparatus and are used in the explanation of the operation thereof.

Referring to FIG. 1, lifting apparatus is shown including magnetic memory devices. Only two magnetic memory devices are shown although it should be noted that a larger or smaller number of such devices could be employed. One device comprises a permanent magnet 10 disposed between a pair of substantially planar pole pieces 12 and 14 adjacent respectively the North and the South poles of the permanent magnet 10. The other permanent magnet device is similar and includes a permanent magnet 16 sandwiched between a pole piece 18 disposed adjacent the South pole of the permanent magnet 16 and a pole piece 20 disposed adjacent the North pole. A control winding 22 having input terminals 24 and 26 is disposed about the center pole members 14 and 18. Additional control windings could be added of course if desired at different positions it convenient for design purposes. The permanent magnets 10 and 16 may, for example, be the well known ceramic type. The pole piece members 12, 14, 18 and 20 may comprise a soft magnetic material. The magnetic device has two ends at which magnetically attractive forces will develop. Theseends will be termed a load end 28 and a keeper end 30. At the load end 28, the pole members 12, 14, 18 and 20 are shown tapered to concentrate the magnetic force. The permanent magnets and pole members are secured together by any convenient means.

A load 32 which may comprise any magnetically attractive material such as iron or steel is shown disposed adjacent the load end 28 of the magnetic devices. A keeper member 34 is disposed adjacent the keeper end 30 of the magnetic devices. The keeper member 34 may comprise a soft magnetic material similar to those of the pole members. A lifting loop 36 is secured to the keeper member 34, for example, by welding. A lifting hook may thus be inserted in the lifting loop 36 and be utilized in conjunction with an external hoist to move and position the lifting apparatus.

A pair of safety members 38 and 40 having an L-shape are secured to the pole pieces 12 and 20 at their external surfaces. The safety members 38 and 40 may be secured to the pole members 12 and 20 respectively by welding, bolting or other convenient methods. The safety members comprise a non-magnetic material, for example, brass or non-magnetic stainless steel. A- stop portion 42 and 44 which extends over a portion of the keeper member 34 is provided in the safety members 38 and 40. Thus, when the keeper member 34 is lifted vertically it will move a distance away from the keeper end 30 of the magnetic devices and then will engage the stop portions 42 and 44 of the safety members 38 and 40. Other means of securing the safety members to the permanent magnet devices could of course be employed.

In the condition shown in FIG. 1, the lifting apparatus is being positioned over the load 32 and is at the instant pictured a distance 6, away from the load end 28. The distance G, will be termed the load air gap which will have a minimum value when the load end 28 abuts against the surface of the load 32. The keeper member 34 is shown abutting against the top surface 30 so that an air gap G exists therebetween. When the keeper member 34 and the end portion 30 are abutting, a minimum keeper air gap exists. When the keeper 34 is separated from the end 30 and abuts against the stop portions 42 and 44, a maximum keeper air gap will exist.

A load magnetic circuit is established from the North poles of the permanent magnets and 16, through the pole members 12 and 20, the air gap G the load 32, the air gap G the center pole members 14 and 18, to the South pole of the permanent magnets. A magnetic flux B will flow through the load magnetic circuit.

A keeper magnetic circuit is established with a magnetic flux B flowing from the North poles of the permanent magnets 10 and 16, through the outer pole members 12 and 20 in the opposite direction to the magnetic flux B through the air gap G the keeper member 34, the air gap B and back to the South poles of the permanent magnets 10 and 16 through the center pole members 14 and 18 in the opposite direction to the magnetic flux B The magnitude of the attractive force applied to the load 32 or the keeper 34 will depend upon the amount of magnetic flux B or B; passing through their respective magnetic circuits.

Assume initially that the keeper member 34 is placed adjacent the end 30 of the magnetic device so that there is a minimum keeper air gap G and that the load 32 is separated from the end 28. The majority of the magnetic flux provided by the permanent magnets will align itself into the keeper circuit so that the keeper 34 will be held by a relatively strong magnetic force to the end 30. With the lifting apparatus in the state shown, the apparatus may be positioned over the load 32 and may be lowered to abut against the top surface of the load. Since the majority of the magnetic flux had previously been aligned in the keeper circuit including the keeper member 34, the keeper member will be held against the end 30 of the device still with a relatively high attractive force while the load 32 will only be held to the end 28 with a relatively small attractive force as determined by the amount of flux B which will pass therethrough. The mechanism by which the flux alignment takes place is discussed in full detail in the above copending applications which are incorporated by reference herein.

In order to switch the high attractive force from the keeper 34 to the load 32 so that the load may be lifted, it is necessary that a majority of the flux supplied by the permanent magnets 10 and 16 be realigned to pass through the load 32 rather than the keeper 34. This may be accomplished by applying a control signal momentarily to the control winding 26. The control signal may be a unidirectional low intensity signal applied in such a direction as to oppose the flux B flowing in the pole pieces 14 and 18. The induced flux caused by the coil 22 in bucking the flux from the permanent magnet will thereby increase the reluctance of the keeper magnetic circuit. The keeper magnetic circuit having an increased reluctance will cause a large percentage of the flux from the permanent magnets 10 and 16 to be transferred from the keeper magnetic circuit to the load magnetic circuit. This flux transferral will thereby switch the high attractive force to the load end 28 of the permanent magnet device so that the load member 32 will be held thereto with a high attractive force. The load 32 will now be held by a high attractive force while the keeper member 34 is free to move vertically if a mechanical force is applied thereto. It should be noted that all that was required to switch the lifting apparatus from a no lift to lift state was the application of a low energy DC. signal to the control signal which may be supplied by a low voltage battery. It should also be observed that the control pulse need only be momentarily applied to the control windings and then may be disconnected therefrom. The momentary application of the control signal is eifective to accomplish the flux trans- 22 through the terminals 24 and fer back and forth between the keeper and load magnetic circuits.

When a mechanically lifting force is applied to the lifting loop 36 to move the keeper member 34 vertically, the keeper member 34 will move until its top portion engages the stop portions 42 and 44 of the safety members 38 and 40. At this point, the air gap G is at a maximum. Several advantages result from having maximum and minimum air gap positions for the keeper 34 with respect to the end 30 of the permanent magnet devices. One of the advantages of the variable air gap is that when maximum keeper air gap exists, that is, when the load is being lifted, a high magnitude lifting force will appear at the lifting end 28 of the permanent magnet devices since the load magnetic circuit is of a very low reluctance in comparison to the keeper magnetic circuit having the maximum keeper air gaps G Thus, a larger attractive force is developed to attract the load 32 than otherwise would be provided if the keeper air gap were constant which has the obvious advantage of permitting larger loads to be moved. Also, as shown in FIG. 1, the permanent magnets 10 and 16 may be positioned closer to the load end than the keeper end in order to increase the attractive force at the load end. Another advantage of having a variable keeper air gap G is that minimum control power is only required to switch the high attractive forces between the load and the keeper and vice versa when the air gap G is at a minimum. This may be seen since when the keeper 34 is adjacent the end 30 a relatively low reluctance path is provided, and, therefore, a relatively low intensity input signal applied to the coil 22 will have a greater effect in either aiding or opposing the permanent magnet flux B in the keeper circuit. Thus, during the positioning operation when the keeper magnetic circuit is in its low reluctance state and adjacent the end 30, when the permanent magnet devices are disposed over the load 32, a low intensity control signal applied to the control winding 22 in a direction to oppose the keeper flux B will readily switch the low reluctance path to that including the load 32 so that the load may be lifted. Alternately, when the moving operation is over and it is desired to disengage the load, with the keeper 34 having been lowered to be adjacent the keeper end 30 at minimum keeper air gap G a low intensity control signal in the opposite direction to the previous signal in a direction to induce a flux which will aid the keeper flux B will readily permit the flux supplied by the permanent magnets 10 and 16 to switch from the load 32 to the keeper 34 and thereby permit the load to be disengaged from the lifting apparatus. The lifting apparatus may then be moved to other areas with the keeper 34 being held against the end 34 by a relatively strong attractive force.

Still another advantage of the variable keeper air gap is that when the keeper air gap is at a maximum value during the lifting operation with the keeper member 34 adjacent the stop portions 42 and 44, the accidental application of switching signals to the coil 22 will not drop the load. Normally, if keeper 34 were abutting the end 30, the load would drop since the high attractive force would be transferred from the load to the keeper. However, with a maximum air gap G existing during the lifting operation when the load'is carried above surface level, the normal low intensity switching signal will not be of sufficient strength to effect the transfer of flux from the load circuit to the keeper circuit. The maximum keeper air gap G can be so designed to set in a safety factor to insure that even an accidental signal applied to the control winding 22 of several times the normal necessary switching magnitude at minimum air gap G will not be effective to transfer the strong attractive force from the load to the keeper and thereby drop the load. It can thus be seen that a fail safe type of lifting apparatus is provided by the apparatus shown 'in FIG. 1.

In FIGS. 2, 3, 4 and 5, a sequence of the lifting and disengaging operations are shown. In FIG. 2, the lifting apparatus is being lowered over a load 32 resting on a surface. The keeper member 34 is held by a relatively strong attractive force, that is, one at least sufficiently strong to permit the keeper 34 to remain adjacent the keeper end 30 of the permanent magnet devices while the lifting apparatus is being positioned over a load. Under these conditions, a majority of the flux from the permanent magnets and 16 pass through the keeper magnetic circuit. The lifting apparatus is shown disposed over the load 32 in FIG. 3. By the application of a DC. control signal, for example, from a battery to the winding 22, a majority of the flux from the permanent magnets is transferred from the keeper magnetic circuit to the load magnetic circuit. Such a transfer of flux may be effected by the application of a low intensive voltage of a polarity as shown on the diagram which will oppose the flux in the keeper magnetic circuit and therefore increase the reluctance thereof so that a majority of the flux may realign itself to pass through the load 32. A high attractive force having the capability of lifting the load 32 will thus be applied at the end 28 adjacent the load 32.

In FIG. 4, the lifting apparatus is shown lifting the load 32 above the surface level. At this point, the keeper member 34 has moved away from the keeper end 30 of the magnetic devices since only a relatively small attractive force is applied at that end. By the application of mechanical force through the lifting loop 36 on the keeper member 34, the keeper will move away from the end 30 until it engages the stop portions 42 and 44 of the non-magnetic safety members 38 and 40. When the keeper member 34 abuts against stop members 42 and 44, a maximum attractive force is developed at the end 28 of the permanent magnet devices to strongly hold the load by a strong attractive force thereto. Also at this maximum air gap position, the accidental application of a control signal that would normally switch the flux back to the keeper member will not be effective because of the maximum air gap. Therefore, the load cannot be dropped :by the application of a control signal accidentally to the coil 22. Hence, the device is fail safe.

The load 32 is shown having been moved and ready for disengagement in FIG. 5 after the load 32 has been brought to surface level. The keeper member 34 then drops from its maximum air gap position to its minimum air gap position abutting against the end 30 of the permanent magnet devices. At the minimum keeper air gap position G the application of a low intensity control signal of the polarity as shown in FIG. 5 will induce a flux to aid the flux through the keeper magnetic circuit and thereby reduce its reluctance to a level lower than that of the load 32. A majority of the flux from the permanent magnets 10 and 16 will align themselves to pass through the keeper circuit now causing a relatively high attractive force to be transferred from the load 32 to the keeper 34. In this condition, the lifting apparatus may be disengaged from the load and moved to other load positions, with the pickup and dropping operations being repeated.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in details of construction and combination and arrangement of parts and elements may be resorted to without departing from the scope and spirit of the present invention.

We claim as our invention:

1. In magnetic lifting apparatus for moving magnetic loads and being operative with control signals, the combination of: a permanent magnet device including a permanent magnet for supplying magnetic flux, a pair of pole members, said permanent magnet being dis- 6 posed between said pair of pole members for providing a first and a second magnetic circuit respectively through a load and a keeper end of said device, and a control winding disposed in at least one of said magnetic circuits for controlling the attractive force at said load and keeper ends of said device in response to control signals being applied thereto; a non-magnetic safety member connected to said pole pieces and having a stop portion thereon; a keeper member disposed at said keeper end of said magnetic device between said device and the stop portion of said safety member in said first magnetic circuit, said load being movable by disposing said keeper member adjacent said keeper end of said device and disposing said load adjacent said load end thereof in said second magnetic circuit and by applying a control signal to said control Winding to transfer a strong attractive force to said second magnetic circuit so that said load is held to said magnet device at said load end thereof by a .strong attractive force, said keeper member moving away from said keeper end of said magnetic device until engaging the stop portion of said safety member so that the inadvertent application of a control signal to said control winding will not drop said load.

2. In lifting apparatus for moving loads the combination of: a permanent magnet device including a permanent magnet for supplying magnetic flux, a pair of pole members, said permanent magnet being disposed between said pair of pole members for providing at least two magnetic circuits respectively through a load and a keeper end of said device, and a control windingdisposed in at least one of said magnetic circuits for controlling the attractive force at said load and keeper ends of said device in response to control signals being applied thereto; a safety member secured to said magnet device and having a stop portion thereon; said load disposed for moving at said load end of said magnet device in one of said magnetic circuits; a keeper member disposed at said keeper end of said magnetic device, said load being movable by applying a control signal to said control Winding to transfer a strong attractive force to the magnetic circuit including said load, said keeper member moving away from said keeper end of said magnet device until engaging the stop portion of said safety member so that the inadvertent application of a control a signal to said control winding will not transfer the strong attractive force away from said load.

3. In magnetic lifting apparatus for moving magnetic loads and being operative with a source of control signals, the combination of: a permanent magnetic flux transfer device including a permanent magnet for supplying magnetic flux, a pair of pole members, said permanent magnet being disposed between said pair of pole members for providing a first and a second magnetic circuit respectively through a load and a keeper end of said device, with the magnetic flux dividing between said magnetic circuits according to their relative reluctance, and a control winding disposed in at least one of said magnetic circuits for controlling the reluctance thereof in response to control signals being applied thereto; said load disposed for moving at said load end of said magnetic device in said first magnetic circuit with a load air gap being formed between said load and said pole pieces at said load end of said device; a keeper member movably disposed at said keeper end of said magnetic device, with a keeper air gap being formed between said keeper member and the pole pieces at said keeper end of said device; and safety means connected to said device to prevent the inadvertent dropping of said load; said apparatus operative for moving said load by disposing said load and said keeper members adjacent said load and keeper ends of said device respectively so that said load and keeper air gaps are a minimum and by applying a control signal to said control winding to transfer a majority of the magnetic flux to said first magnetic circuit with said load being held to said magnet device by a strong attractive force, said load being movable by the application of mechanical force to said keeper member so that said keeper member moves away from said keeper end of said magnetic device until being restricted by said safety means, said keeper air gap being a maximum when said keeper member is restricted by said safety means so that the inadvertent application of a control signal to said control winding will not transfer sufiicient flux to said keeper member to drop said load.

4. In magnetic lifting apparatus for moving magnetic loads and :being operative with control signals, the combination of: a permanent magnetic flux transfer device including a permanent magnet for supplying magnetic flux, a pair of pole members, said permanent magnet disposed between a pair of pole members for providing a first and a second magnetic circuit through a load and a keeper end of said device, with the magnetic flux dividing between said magnetic circuits according to their relative reluctance, and a control winding disposed in at least one of said magnetic circuits for controlling the reluctance thereof in response to control signals being applied thereto; a non-magnetic safety member secured to said pair of pole pieces of said magnetic device and having a stop portion thereon; said load disposed for moving at said load end of said magnetic device in said first magnetic circuit with a load air gap being formed between said load and said pole pieces at said load end of said device; a keeper member disposed at said keeper end of said magnetic device between said device and the stop portion of said lifting member with a keeper air gap being formed between saidkeeper member and the pole pieces at said keeper end of said magnetic device; said apparatus operative for moving said load by disposing said load and said keeper member adjacent said load and keeper ends respectively of said device so that said load and keeper air gaps are a minimum and by applying a control signal to said control winding to transfer a majority of the magnetic flux to said first magnetic circuit with said load being held to said load end of said magnet device by a strong attractive force, said load being movable by the application of mechanical force to said keeper member so that said keeper member moves away from said keeper end of said magnetic device until engaging the stop portion of said safety member, said keeper air gap being a maximum when said keeper member engages said stop portion so that the inadvertent application of a control signal to said control winding will not transfer suflicient flux to said keeper member to drop said load.

References Cited by the Examiner UNITED STATES PATENTS 5/1963 Cotton de Bennetot 317-163 X 8/1964 Moreau 317-172 X 

3. IN MAGNETIC LIFTING APPARATUS FOR MOVING MAGNETIC LOADS AND BEING OPERATIVE WITH A SOURCE OF CONTROL SIGNALS, THE COMBINATION OF: A PERMANENT MAGNETIC FLUX TRANSFER DEVICE INCLUDING A PERMANENT MAGNET FOR SUPPLYING MAGNETIC FLUX, A PAIR OF POLE MEMBERS, SAID PERMANENT MAGNET BEING DISPOSED BETWEEN SAID PAIR OF POLE MEMBERS FOR PROVIDING A FIRST AND A SECOND MAGNETIC CIRCUIT RESPECTIVELY THROUGH A LOAD AND A KEEPER END OF SAID DEVICE, WITH THE MAGNETIC FLUX DIVIDING BETWEEN SAID MAGNETIC CIRCUITS ACCORDING TO THEIR RELATIVE RELUCTANCE, AND A CONTROL WINDING DISPOSED IN AT LEAST ONE OF SAID MAGNETIC CIRCUITS FOR CONTROLLING THE RELUCTANCE THEREOF IN RESPONSE TO CONTROL SIGNALS BEING APPLIED THERETO; SAID LOAD DISPOSED FOR MOVING AT SAID LOAD END OF SAID MAGNETIC DEVICE IN SAID FIRST MAGNETIC CIRCUIT WITH A LOAD AIR GAP BEING FORMED BETWEEN SAID LOAD AND SAID POLE PIECES AT SAID LOAD END OF SAID DEVICE; A KEEPER MEMBER MOVABLY DISPOSED AT SAID KEEPER END OF SAID MAGNETIC DEVICE, WITH A KEEPER AIR GAP BEING FORMED BETWEEN SAID KEEPER MEMBER AND THE POLE PIECES AT SAID KEEPER END OF SAID DEVICE; AND SAFETY MEANS CONNECTED TO SAID DEVICE TO PREVENT THE INADVERTENT DROPPING OF SAID LOAD; SAID APPARATUS OPERATIVE FOR MOVING SAID LOAD BY DISPOSING SAID LOAD AND SAID KEEPER MEMBERS ADJACENT SAID LOAD 